It wasn't so much that it was put in stuff that wasn't useful it was more that it was put in stuff that needed something better than Bluetooth but they put in Bluetooth because it was new and shiny rather than old boring radio.

The problem with Bluetooth, especially back then, was that the range was terrible (about 1 ft in my experience), you couldn't connect to more than one thing at a time, it consumed quite a lot more power than radio (we have ultra low power modes now), and the bandwidth wasn't great either (still somewhat the case but the bandwidth has improved). So you had things like Bluetooth car keys which were like keyless entry systems we have today, but rather than using radio they used Bluetooth so half the time you'd go near your car and nothing would happen.

A lot of the cases where things used to have Bluetooth now use Wi-Fi today. Of course there were always things that had Bluetooth for a gimmick, but the vast majority of it was simply things that had Bluetooth when something else would have been the better option. Back then Bluetooth headphones were seen as a gimmick because they basically didn't work, now they work, so they're not a gimmick anymore. The perception of if something is or is not a gimmick is more about if it works rather than if it actually is a useful product.